1. Field of the Invention
The present invention relates to the field of automated testing of computer equipment, more particularly, to an improved method for testing computer hard disks.
2. Description of the Related Art
Personal computers have become increasingly more powerful during the recent years and are utilized for a variety of applications in industry, business and education. The varied uses result in different requirements for various subsystems forming the complete computer system. With the increased performance of computer systems, it became apparent that mass storage subsystems, such as fixed or hard disk drives, played an increasingly important role in the transfer of data to and from the computer system.
The reliability of the hard disk drive systems is critical to the operation of computer systems. Thus, it is preferable that a hard disk drive system be thoroughly tested prior to sale of the disk drive and/or computer system incorporating the disk drive. This test procedure generally includes multiple writes and reads to sectors on the disk drive. These multiple writes/reads are used to identify errors on the disk which indicate that certain sectors on the disk cannot be reliably written or read. These errors may arise from defects in the disk media, the disk heads, disk servo mechanisms, noise or other sources. While it is preferable that a disk have no errors associated with it, as a practical matter, disk drives often have various errors, such as media errors, due to manufacturing processes, handling or other causes.
Recognizing this, disk drive manufacturers have established various acceptable error rates for disk drives. Error rates are a measure of the disks ability to consistently read and write data. As a practical matter, it is often difficult to determine the cause producing the error without significant statistical analysis. However, the data required to perform the statistical analysis is often not recorded during the disk test procedure. The acceptable error rates may be expressed as total numbers of errors for a given number of bytes, maximum acceptable errors of any type of error, or the total number of errors occurring for a given number of bytes read.
The error rates specified by disk manufacturers generally account for all disk media errors prior to shipping to the computer manufacturers. Any media errors which are detected by the disk manufacturers are generally mapped out or reallocated to alternate sectors on a disk. It will be appreciated that the design of hard disk drives often permits the creation of extra sectors which may be utilized for the reallocation process. This permits the disk manufacturers to supply the hard disks as being error free. Disk manufacturers utilize other techniques to compensate for any disk errors which may occur. One method of compensation of errors during the transmission of data is through the use of various error correction code (ECC) formats, which are known in the art. The use of ECC codes has evolved such that the disk drive controllers often perform data correction as the data stream is being read, with the computer system not even being aware of the error.
However, a manufacturer's test may not account for defects which may arise following the manufacturer's test and prior to the integration of the disk as part of a computer system. Thus, it is prudent for the computer manufacturer using the hard disk to carry out its own tests of the hard disk.
Typically, the computer manufacturer performs a disk drive test as part of a final extended burn-in test following assembly. During the burn-in, the computer system executes various test routines which are designed to exercise the various computer subsystems including disk subsystems, video subsystems and memory. These burn-in test procedures often last in excess of 72 hours. During this period, the disk test routine will write and read multiple times to the tracks on the disks and total the number of errors which occur during the disk reads. The test generally entails writing various data patterns to random and/or sequential disk tracks on the drive under test. The data patterns and track selection methods used are intended to find potential structural and electrical faults within the disk drive which may occur during everyday operation.
The disk test is generally executed for a fixed period of time, and the number and type of disk errors which occur during the burn-in are then compared with manufacturer set error rates for that type of disk upon completion of the burn-in test. The standards are generally in terms of errors of specific types for a given number of bytes read from the hard disk. Generally, the total number of bytes read is estimated based on the number of hours the disk test has been running. The disk or disks are then passed or failed based on the number of accumulated errors after the test has been completed. When the disks fail, they are generally replaced and the computer unit must again go through the full burn-in cycle.
It will be appreciated that a disk or disks may exceed the acceptable error level for the type of disk early during the burn-in test cycle. Nonetheless, the disk will continue to undergo the disk burn-in tests for the designated time period. This method of testing disk can result in considerable unwarranted manufacturing time and cost where the disk drive may fail early during the burn-in test. Further, present disk test methods often fail to distinguish between the various types of disk errors occur, which may lead to rejection of disk drives which are otherwise serviceable.
Computer manufacturers often utilize disk drives of various types, thereby complicating the task of performing the disk tests. Disk drives used within computer systems may vary as to the type of interface employed, such as Small Computer Standard Interface (SCSI) or Enhanced Small Disk Interface (ESDI) drives; the number of heads, cylinders, tracks and sectors per track for the disk; whether the disk utilizes ECC correction techniques or includes a bad sector map in a reserved area on the disk; and whether the disk employs hardware improvements, such as a memory cache located on the disk drive. A computer manufacturer's testing procedure must account for the various types of disk hardware utilized within its product line.
Thus, there exists a need for a dynamic method of measuring and recording disk error rates during a disk drive testing procedure. Further, there exists a need for a method of characterizing the types of disk errors which may occur, to permit further statistical analysis of repeated failures of a disk drive.